Prosecutors have rejected the guilty pleas of two women caught trying to smuggle 11kg of cocaine out of Peru in their luggage.

Michaella McCollum, 20, from County Tyrone, Northern Ireland, and Melissa Reid, 20, from Glasgow, pleaded guilty on Tuesday behind closed doors when they appeared before a judge in Callao, near the capital Lima.

Prosecutors have asked for more information before accepting their admissions of guilt, which the women hope will reduce their sentences from a minimum eight years down to six years and eight months without the chance of parole.

A spokesman for the prosecutors' office in Callao said: "The two drug mules' guilty pleas have not been fully accepted, as far as the prosecutor is concerned, until they give more details. They will be asked to give another statement before the judge explaining where the drugs came from, who supplied them and why they said they had been forced to carry them by an armed gang."

The spokesman said a date was still to be determined for a new hearing, although after their guilty pleas, officials said the women would be sentenced on 1 October.

Both women, who had been working on the Spanish party island of Ibiza this summer, have been held at the harsh Virgen de Fatima prison in Lima.

Court officials have said they may be transferred to the equally tough Santa Monica women's jail once they are sentenced. Prosecutor Juan Rosas told reporters on Wednesday: "The prosecution thinks the charges have not yet been completely embraced." They have simply accepted transporting drugs, but what has not yet been examined is their original version that they were kidnapped or were transporting the drugs against their will.

"As far as the prosecution is concerned, these citizens were never kidnapped, were never threatened or coerced.

"If they stick to that unbelievable story the prosecution is not going to allow them the benefit of a guilty plea."

He disputed a statement issued on Tuesday by the court where the women entered their plea that said they had provided information on their co-conspirators.

Their guilty pleas came on the same day that the UN declared that Peru has now overtaken Colombia as the world's number one coca leaf producer.

According to a report by the United Nations Office on Drugs and Crime, coca plantations in Peru covered 60,400 hectares last year.